When they were born, Abigail and Brittany Hensel’s parents were told they probably wouldn’t survive for more than a few hours. Their case is rare. The twins have two hearts, two sets of lungs, two stomachs, and two separate brains. However, they were born with dicephalic parapagus. This means that they were born with two heads but just one body. From the waist down they share all organs. Brittany controls the left side of their body, while Abigail controls the right. The University of Maryland Medical Center reports that “conjoined twins occur once every 200,000 births.”In order to understand the lives of conjoined twins, one must first understand how this phenomenon occurs,  separation procedures, and the ethical issues that ensue.First, it is important to understand how conjoined twins occur. According to the Encyclopedia of Diseases and Disorders, conjoined twins are identical twins where the two embryos did not separate completely before the baby was born. The disorder results from the failure of the embryos to split after the twelfth day of the fetus’s development. When a fertilized human egg manages to divide before the twelfth day, the twins will be born separately. The longer the embryos take to split, the more complicated the interconnection of the infant’s body will be. The University of Maryland Medical Center states, “about 40 to 60% of conjoined twins arrive stillborn, and about 35 % survive only one day. The overall survival rate of conjoined twins is somewhere between 5 % and 25 %.” Female siblings seem to have a better shot at survival than their male counterparts, females are three times as likely as males to be born alive. About 70 % of all conjoined twins are girls.Secondly, In most cases, the separation surgery will occur once the twins become 4 months old. The waiting gives the infant’s body a chance to grow. This makes it easier for the doctors to perform the surgery and makes the surgery easier on the infant’s body. According to the American Pediatric Surgical Association. only roughly 250 separation surgeries have ever been successful, this means that at least one twin survived over a long period of time. There are several different categories of conjoined twins, which means each separation procedure is different. According to Medscape, which is a leading medical resource for physicians, medical students, nurses, and other healthcare professionals, 74% of conjoined twins are connected at the chest, abdomen, or both.  In order to split twins that are joined at the torso, the surgeon first breaks through the skin, then must carefully split the organs and give enough of the organ to both bodies, making sure to avoid major arteries and veins. The cut organs are then stitched up and placed back into the individual bodies before the skin itself is stitched together. Lastly, whether or not the twins can successfully be separated depends on how many organs, or how much of an organ they share. Many ethical complications can result from the separation or the decision not to separate. The decision to separate conjoined twins would be made easy if survival of both individuals was guaranteed, however, this is not always possible. In some cases, separation would result in severe health risks for one, or both, of the twins. One example of this occurred in two-year-old twins connected at the head. The girls, who were unnamed, shared their kidneys and the veins that regulate blood in their brains. The separation surgery was very unlikely to benefit both twins. However, leaving them joined could also threaten their health. The odds of both twins surviving separation surgery was 33%. According to the UH Case Medical Center in Cleveland, after the completion of the risky surgery, the larger twin would need a kidney transplant or life-long dialysis to live and the smaller twin would be at risk for brain damage. But left together, the girls were at risk for kidney failure and cardiovascular disease. In several cases, the parents have to make a decision of whether or not to risk the twins lives by making the split. Sometimes the parents must even make the decision to sacrifice a twin that has a small chance of survival, in order to save the healthier one.Understanding how conjoined twins are created, surgery for separation, and ethical issues that can result, is fundamental in learning about their lives. Like Abby and Brittany,  several conjoined twins live happy, healthy lives, whether they are separated or not.